We propose a program of research on the localization and analysis of genetic determinants on human chromosomes, as well as subchromosomal structural changes underlying diseases, with emphasis on the human X, #15, #21, and other regions of the genome in which abnormalities can be associated with mental retardation and/or developmental defects. The research planned utilizes techniques which allow intense study of subchromosomal regions, such as fluorescence activated chromosome sorting and phenol-enhanced differential hybridization, recombinant DNA methodology, cytogenetics, somatic cell genetics and pedigree analysis. The goal is to obtain, localize, and characterize cloned DNA segments, as well as deleted, duplicated, rearranged, or labile subchromosomal regions associated with specific diseases. Using Xp21 deletions in DMD as a prototype and starting point, we will explore adjacent regions and deletions responsible for glycerol kinase deficiency, the McCloud phenotype, as well as X- linked eye diseases such as retinitis pigmentosa, retinoschisis, and choroideremia, the last associated with a deletion in proximal Xq. Structural analysis of Xp21, as well as distal Xp and Xp will be used to study normal and abnormal meiosis and the role of the latter in deletion-related diseases, insertion of a Yp segment into Xp in 46,XX males, and aneusomy. Recombination based screening will be used to obtain molecular probes near the fragile site in distal Xq to study its structural features and unusual mode of mutation. Existing and newly sought molecular probes will be used to analyze MR-associated diseases in 12p and proximal 15q1, in the case to understand better the nature and causes of structural changes associated with the Prader-Willi syndrome, as well as to refine diagnosis of this disease. Other genomic probes, as well as antibodies, will be used to isolate cDNA sequences mapping to chromosome #21 to investigate abnormalities, related to Down syndrome, of tissue-specific #21 DNA expression, e.g. as regards neuronal organization and cell surface changes underlying developmental defects. Of particular interest will be #21-linked amyloid beta protein cDNA and the relationship of amyloid to premature aging in Down syndrome and to Alzheimer disease. The information sought should both be of basic mechanistic interest, and it should translate readily into practical molecular genetic diagnostic applications.